Backyard Aquaponics
A place to discuss aquaponics

After losing my entire tank of 8 month old tilapia to a power cut earlier this year. A few weeks ago we went and got a load more. We have about 50 fingerlings in a small system indoors and that is going fine, we also picked up 15 large tilapia to go in our aquaponic greenhouse. The greenhouse tank previously had fingerlings in before the big fish so it was fully cycled and working.

Sadly my big fish seem to be mysteriously dying. I had 1 dead yesterday and 2 dead this morning. None had died since we got them.

They look very healthy and are eating fine.
The water stays between 26ºC and 28ºC.
The water is almost clear and there are 2 aerators (the tank is only about 170 litres).
And the grow beds have healthy plants growing in them.

The only different thing is the pH has dropped from 7 to about 6.5.

Should I do a water change?

I have ordered an ammonia testing kit to see if it that but I am seriously worried about the rest of my fish. Any ideas what it could be and what I should do?

Thank you vey much!

Sounds like a lot of fish for only 170L. I would guess your test kit will show high ammonia and nitrite levels. Suggest daily water changes and dosing with salt.